Study claims evidence of a link between pesticide use and autism

But small numbers and lots of tests raise questions about significance.

Autism has a strong genetic component, and, even in cases that aren't inherited, newly formed mutations appear to be common. But genetics isn't everything, raising questions about exactly what the environmental influences are. A variety of factors have been suggested, ranging from immune disorders to environmental toxins.

One of the factors that has been suggested is pesticide use. These chemicals, which typically target the nervous system of insects, can also be toxic to humans. Exposure has been associated with some disorders of the nervous system, most notably Parkinson's disease. Now, a study is out suggesting that autism is also associated with pesticide exposure. But the study has some pretty significant limitations, so it shouldn't be viewed as anything more than a reason to work on a more thorough study.

Further Reading

Researchers have now sequenced every protein coding gene in groups of autism …

The study relies on a group of infants termed the Childhood Autism Risks from Genetics and Environment (CHARGE) study population. These children are recruited when they register with the state social services; matched controls are recruited at the same time.

The ability to track pesticide use comes from California environmental regulations, which require that any commercial pesticide use, along with its location, be registered with the state. That location can then be compared to the residence of the parents of children in the CHARGE study. This provides a very rough indication of potential pesticide exposure.

The authors of the paper, who are all based in California, managed to get data for 970 children, which seems like a reasonable number. But a sizable majority of them (70 percent) had no exposure. The remainder were then split into individual groups based on their proximity to the pesticides being used, with the distances set at 1.25km, 1.5km, and 1.75km. (The reasoning behind using these distances isn't made clear in the text.) Then, the groups were further divided based on which of five classes of pesticides were used in the area.

There are two consequences to all this dividing. One is that the populations get very small. For three of the pesticides, the total number of autistic individuals who might have been exposed at any distance was in the area of 50 to 60 people.

The other problem is that you end up with a lot of tests. The authors look at exposure during the period immediately before conception, the entire pregnancy, and in each of the three trimesters. That's five conditions, multiplied by three distances to give 15 individual tests for each pesticide. They also look at four pesticides for a total of 60 tests. There are actually 63, since a fifth pesticide was only tested with the entire pregnancy, as the number of individuals exposed was too small. Then, they repeat the entire process for developmental delay.

That's 126 different tests. Which means the odds of a spurious positive result are rather high.

In the end, most of these tests come out negative. There are some very weak positive associations with organophosphates late in pregnancy. There's a somewhat stronger result with Chlorpyrifos, but the association actually increases as the distance to the site of use goes up. And then there are a couple of barely significant results scattered through the remainder of the tests. Results with developmental delay appear similar in that the few significant ones are weak and don't display any particular pattern.

The authors conclude that their work "strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures." But really, the study mostly indicates that a link can't entirely be ruled out. A larger, more focused study might be able to determine if any of these results are more than a statistical fluctuation.

The one thing that popped out at me (besides everything else that was mentioned), was their idea of exposure to a pesticide. Just because someone 1 mile down the road used a pesticide doesn't mean that any of it ever actually came into contact with you. What if a golf course was a km down the road, but downwind (prevailing winds) and a direction you never travel? What if it's across the street and every time they mow you're surrounded by dust? Those 2 would be counted as the same level of exposure according to this study.

The one thing that popped out at me (besides everything else that was mentioned), was their idea of exposure to a pesticide. Just because someone 1 mile down the road used a pesticide doesn't mean that any of it ever actually came into contact with you. What if a golf course was a km down the road, but downwind (prevailing winds) and a direction you never travel? What if it's across the street and every time they mow you're surrounded by dust? Those 2 would be counted as the same level of exposure according to this study.

That's because the authors most likely aren't interested in finding the correct results, only results that agree with their preconceived notions.

Could we have a discussion about the article itself and the study cited within it instead of the same of "OMG JENNY MCCARTHY" and "OMG ANTI-VAXXERS" rants? The ArsTechnica article isn't about either Jenny McCarthy or vaccines, and I think it's an interesting study.

EDIT: Ars spends one sentence on the study's finding and the rest of the time asserting methodological shortcomings of the study, but without having read other articles, it's not clear from the Ars article what exactly the study found. So for anyone curious, from Time.com, the study found a statistical correlation between exposure to home pest sprays during pregnancy and autism rates:

Quote:

Living near a spraying of pyrethroids, which are commonly found in home insect sprays, just before conception or during the third trimester of pregnancy increased by up to two-fold the risk of both ASDs and developmental delays.

The authors conclude that their work "strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures." But really, the study mostly indicates that a link can't entirely be ruled out. A larger, more focused study might be able to determine if any of these results are more than a statistical fluctuation.

Now if Ars can manage to apply a similar dose of healthy skepticism every time it reports the results of a new study -- especially when that study confirms the personal preconceptions of the editorial staff -- we'll really be getting somewhere.

I'm torn. This will stir up the fanatics like crazy. However, unlike vaccines, some pesticides are doing a lot of damage, so this could help the push to ban things that might be killing bees. Then again, it could cause fanatics to protest safe pesticides that help us feed their fanatical faces.

The authors conclude that their work "strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures." But really, the study mostly indicates that a link can't entirely be ruled out. A larger, more focused study might be able to determine if any of these results are more than a statistical fluctuation.

Still, I'm glad they did it.

Hopefully now funding will be available for a proper study.

So, to get a proper funded study you first toss a grenade into the room and when the smoke clears a few years down the road and people have been struck off and parents have been given false hopes and vague cures you go and tell the world that it was all just a mistake?

If thats how it works now I'd suggest we've gone down the wrong road somewhere.

I'm torn. This will stir up the fanatics like crazy. However, unlike vaccines, some pesticides are doing a lot of damage, so this could help the push to ban things that might be killing bees. Then again, it could cause fanatics to protest safe pesticides that help us feed their fanatical faces.

Contrary to the header image for the article, the pesticides at issue in this study are primarily found in home pest sprays (like what are found in bug bombs), not agricultural pesticides.

Switching from Orkin to NatureLine to control black widows or roaches...there's not much of a downside to that.

The authors conclude that their work "strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures." But really, the study mostly indicates that a link can't entirely be ruled out. A larger, more focused study might be able to determine if any of these results are more than a statistical fluctuation.

Still, I'm glad they did it.

Hopefully now funding will be available for a proper study.

I'm hoping they did it to generate headlines to get funding for a bigger, better study that can control for all those variables and reach sound, scientific conclusions (or at least correlations).

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It's not crap. If we can't rule out pesticides as a cause for rising autism rates, then it needs to be investigated properly.

Something has caused a 30% increase in autism over the last 24 months.

Something is causing autism to be 1.5% of the united states population but only 0.15% worldwide.

Studies like this are the only way to find out what's going on.

That something is diagnosis and medical treatment. Most of the "epidemic" of autism cases are high-functioning cases. 50 years ago many of these would have been considered sub-clinical. Better medical care has caused these to be diagnosed. .

I'm torn. This will stir up the fanatics like crazy. However, unlike vaccines, some pesticides are doing a lot of damage, so this could help the push to ban things that might be killing bees. Then again, it could cause fanatics to protest safe pesticides that help us feed their fanatical faces.

Contrary to the header image for the article, the pesticides at issue in this study are primarily found in home pest sprays (like what are found in bug bombs), not agricultural pesticides.

Switching from Orkin to NatureLine to control black widows or roaches...there's not much of a downside to that.

Gotcha. I imagine Austism fanatics would skim over the details even more than I did, so don't expect anyone but you, me, and our fellow readers to be this educated on the topic.

Good article by JT. The study is very inconclusive and most results are weak but it may indicate lines of research that would lead to more conclusive results. I'd welcome more directed, rigorous studies with larger samples, whatever the results.

No need to pooh, pooh anything yet. Let's just find out the facts and act accordingly.

Edit: My own opinion is that it is largely a genetic disorder but if environmental factors exacerbate it or lead to new mutations, why not know sooner rather than later?

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It seems to me the study is reasonable in that it filters for correlation, which is what anyone would want to do when looking at a large body of data of unknown value. Is there anything potentially meaningful in the data or not. The answer appears to be a "yes/maybe." Now that a useful correlation has been observed, more work can directed toward qualifying that observation.

It might not be ready for use in policymaking but if I was deciding to use pesticides in a home with a pregnancy or possible pregnancy I might decide to avoid de facto, in vivo testing as not worth the risk.

Could we have a discussion about the article itself and the study cited within it instead of the same of "OMG JENNY MCCARTHY" and "OMG ANTI-VAXXERS" rants? The ArsTechnica article isn't about either Jenny McCarthy or vaccines, and I think it's an interesting study.

EDIT: Ars spends one sentence on the study's finding and the rest of the time asserting methodological shortcomings of the study, but without having read other articles, it's not clear from the Ars article what exactly the study found. So for anyone curious, from Time.com, the study found a statistical correlation between exposure to home pest sprays during pregnancy and autism rates:

Quote:

Living near a spraying of pyrethroids, which are commonly found in home insect sprays, just before conception or during the third trimester of pregnancy increased by up to two-fold the risk of both ASDs and developmental delays.

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It's not crap. If we can't rule out pesticides as a cause for rising autism rates, then it needs to be investigated properly.

Something has caused a 30% increase in autism over the last 24 months.

Something is causing autism to be 1.5% of the united states population but only 0.15% worldwide.

Studies like this are the only way to find out what's going on.

That something is diagnosis and medical treatment. Most of the "epidemic" of autism cases are high-functioning cases. 50 years ago many of these would have been considered sub-clinical. Better medical care has caused these to be diagnosed. .

Maybe.

I think this is probably what's going on, but I've never seen a proper study. So until the study is done, I am all for any study investigating other possibilities.

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It's not crap. If we can't rule out pesticides as a cause for rising autism rates, then it needs to be investigated properly.

Something has caused a 30% increase in autism over the last 24 months.

Something is causing autism to be 1.5% of the united states population but only 0.15% worldwide.

Studies like this are the only way to find out what's going on.

That something is diagnosis and medical treatment. Most of the "epidemic" of autism cases are high-functioning cases. 50 years ago many of these would have been considered sub-clinical. Better medical care has caused these to be diagnosed. .

Whether it is increased diagnosis, broader criteria, or a tendency to diagnose as autism spectrum disorder rather than a non-specific developmental delay due to better funding for treatment that has led to the 'increase', a study that claims to have identified a correlation between proximity to pesticide spraying and autism diagnosis warrants some (critical) attention.

Certainly you need to consider whether they corrected for the number of 'tests' because the more things you check the greater the risk of a false positive result. You also need to consider why they chose the distances they did: if you can calculate using a continuous variable (e.g. raw distance) rather than using a categorical variable (e.g. distance bands) then you have a wider range of tests available to you. Mind you, in this case using a distance could be a problem because there is a much more consequential difference between 1km and 2km than between vs 50km and 100km and that would seriously screw up any linearity of relationship. You can correct for that sort of thing by using log transformations and so on, though.

However, even if what they detected isn't autism, but rather some more general problem being diagnosed as autism (due to all the issues described above about subclinical cases and so on) and the tests are broadly valid, then that still matters and warrants further investigation.

Big studies typically start as pilot studies, and pilot studies have relatively higher error rates (because they are exploratory so often prioritise detection - even if potentially spurious - over potentially missing a real effects).

It makes sense that exposure to toxic substances will have some form of negative impact on people, That said this study has some serious issues, enough so for it to not be definitive nor dismiss-able as nonsense. It might be worth it to do more thorough studies and with samples from other places to confirm or disprove its findings.

I'm torn. This will stir up the fanatics like crazy. However, unlike vaccines, some pesticides are doing a lot of damage, so this could help the push to ban things that might be killing bees. Then again, it could cause fanatics to protest safe pesticides that help us feed their fanatical faces.

Contrary to the header image for the article, the pesticides at issue in this study are primarily found in home pest sprays (like what are found in bug bombs), not agricultural pesticides.

Switching from Orkin to NatureLine to control black widows or roaches...there's not much of a downside to that.

Gotcha. I imagine Austism fanatics would skim over the details even more than I did, so don't expect anyone but you, me, and our fellow readers to be this educated on the topic.

I don't know what an "autism fanatic" is, but I'm the parent of an autistic child and I'm very interested/concerned about what factors can contribute to autism rates, and I get pretty darned furious when every single article with "autism" in the title gets flooded with "Jenny McCarthy" this and "anti-vaxxers" that, even when the article has NOTHING to do with vaccines. It's like people see the word "autism" and start going off on well-practiced rants without even reading a single sentence of the particular article.

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It's not crap. If we can't rule out pesticides as a cause for rising autism rates, then it needs to be investigated properly.

Something has caused a 30% increase in autism over the last 24 months.

Something is causing autism to be 1.5% of the united states population but only 0.15% worldwide.

Studies like this are the only way to find out what's going on.

That something is diagnosis and medical treatment. Most of the "epidemic" of autism cases are high-functioning cases. 50 years ago many of these would have been considered sub-clinical. Better medical care has caused these to be diagnosed. .

Maybe.

I think this is probably what's going on, but I've never seen a proper study. So until the study is done, I am all for any study investigating other possibilities.

Switching from Orkin to NatureLine to control black widows or roaches...there's not much of a downside to that.

Except for the downside of the products not working very well.

We use NatureLine products to treat our house (applied by All Natural Pest Elimination, an Oregon business) and cans of EcoSmart Wasp & Hornet Killer to handle black widows we find in our yard and garden. Both work extremely effectively and are utterly harmless to pregnant women, young kids, small dogs, etc.

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

It's not crap. If we can't rule out pesticides as a cause for rising autism rates, then it needs to be investigated properly.

Something has caused a 30% increase in autism over the last 24 months.

Something is causing autism to be 1.5% of the united states population but only 0.15% worldwide.

Studies like this are the only way to find out what's going on.

It's not so much a rise in actual autism, but a rise in the diagnosis of autism. There are extra sociological & political pressures driving the higher rates of diagnosis in the US. For one, school districts get extra money for "special needs" students, this lowers the threshold of what could be considered full blown autism and just a kid having difficulties or a different learning style. There is also a lot of political pressure in the US by the psychiatric & pharmaceutical industries to get everyone diagnosed with something and into the system of professional care.

The authors conclude that their work "strengthens the evidence linking neurodevelopmental disorders with gestational pesticide exposures." But really, the study mostly indicates that a link can't entirely be ruled out. A larger, more focused study might be able to determine if any of these results are more than a statistical fluctuation.

Still, I'm glad they did it.

Hopefully now funding will be available for a proper study.

Your comment illustrates the problem - thinking that crap like this study is useful for any kind of decision making.

Ok...just to be clear...the book on autism causes is closed? No need for any new studies? Got it.

I do not know what the "adjusted odds ratios" refer to in this paper; I assumed it means odds of autism with exposure relative to non-exposure. Here is the fishy thing: out of 126 trials, only 3 find an adjusted odds of less than 1, even though that ratio falls within 110/126 of the 95% confidence intervals. Unless every pesticide has a very significant impact at all stages of pregnancy (the confidence intervals suggest than only some have at most a moderate impact), the small numbers here should lead to many ratios below 1 just due to statistical fluctuations. This seems to be some terribly biased odds estimator they are using. If your statistical test is biased towards finding odds greater than one, you cannot really draw conclusions when you find odds greater than one....

The fact that many of the pesticide-autism "correlations" show no significant correlation with distance means any conclusion suggesting a link between pesticides and autism (as given by the authors of this paper) should not be made based on this data. It does not rule out pesticides as causing autism, but it much more strongly suggests that there is some other, more important confounding factor.

The authors of the paper, who are all based in California, managed to get data for 970 children, which seems like a reasonable number.

is "seems like a reasonable number" the standard for reporting statistical significance now? Even though the author does go on to explain how the population was split into ever smaller groups which ultimately undermine the overall significance, even the initial group of 970 doesn't "seem reasonable" to me considering autism only impacts about 15 of 1000 people to begin with.

I do not know what the "adjusted odds ratios" refer to in this paper; I assumed it means odds of autism with exposure relative to non-exposure. Here is the fishy thing: out of 126 trials, only 3 find an adjusted odds of less than 1, even though that ratio falls within 110/126 of the 95% confidence intervals. Unless every pesticide has a very significant impact at all stages of pregnancy (the confidence intervals suggest than only some have at most a moderate impact), the small numbers here should lead to many ratios below 1 just due to statistical fluctuations. This seems to be some terribly biased odds estimator they are using. If your statistical test is biased towards finding odds greater than one, you cannot really draw conclusions when you find odds greater than one....

The fact that many of the pesticide-autism "correlations" show no significant correlation with distance means any conclusion suggesting a link between pesticides and autism (as given by the authors of this paper) should not be made based on this data. It does not rule out pesticides as causing autism, but it much more strongly suggests that there is some other, more important confounding factor.

And if the people who did the study were shouting "hey, we've conclusive proved what causes autism!" from the mountaintop, instead of publishing a study showing a potential correlation that should be further investigated through a larger study (for which they're almost certainly seeking funding), I'd have a bigger problem with the fact that their study was small.